Motorola Corporation

Maxim Integrated Products, Inc.

Freescale Semiconductors Inc.

Michael McGinn

Gerald K Lunn

David K Lovelace

W Eric Main

William Eric Main

A temperature compensated bandgap reference circuit includes a bandgap voltage generator having a temperature dependent signal output and a correction circuit coupled to the output of the bandgap voltage generator and generating a second order quadratic signal which is complementary to the signal output.

Bandgap curvature correction circuit for compensating temperature dependent bandgap reference signal

A front end tuning system includes a tuning signal generator. The tuning signal generator includes a digital-to-analog converter (DAC) to receive a pre-conditioned tuning signal at a reference input, to receive a digital value at a digital control input, and to produce a modified tuning signal based on the digital value and the pre-conditioned signal. Preconditioning the tuning-voltage allows a simple current type DAC to be can be used, rather than an 8-bit ladder type DAC used by some other front end tuners. Significant cost savings can be achieved because less memory is required to store the digital values supplied to the DACs, and set up times can be reduced. An adjustable temperature compensation circuit provides additional adaptability.

Tuning signal generator and method thereof

A voltage-to-current converter having improved third order distortion is disclosed herein for use in an FM radio system, particularly an FM radio system which employs a broadband input filter rather than a narrow band input filter. By cross-coupling a main amplifier with a second amplifier that produces more distortion and has a smaller g , than the main amplifier, third order frequency peaks resulting from non-linear amplification of undesired signals can be prevented from interfering with a desired signal because the magnitude of the third order frequency peak is reduced.

System, apparatus and method for voltage to current conversion

An image reject transceiver (10) provides both phase and gain adjustments that causes unwanted images to be rejected. A reference signal (RF.sub.IN) is frequency translated by two mixer circuits (28, 34) in a receiver circuit (16) to provide both an in-phase and an out-of-phase replica signal of the reference signal (RF.sub.IN) during normal operation. In a calibration mode a single frequency generated by a transmitter VCO (22) replaces the reference signal (RF.sub.IN). A phase detector circuit (38) provides a phase difference value that is fed back through a first switch (45) to a phase shift circuit (36) for adjusting the phase separation between the two replica signals. An amplitude detector circuit (40) provides an amplitude error value that is fed back through a second switch (47) to the mixer circuit (34) for adjusting and matching the gain of the two replica signals.

Image reject transceiver and method of rejecting an image

An image reject receiver (10) uses a mixer circuit (12) and a mixer circuit (16) to frequency translate an incoming reference signal (RF.sub.IN) and generate a first output signal (V.sub.OUT1) and a second output signal (V.sub.OUT2), respectively. Two phase detectors (26 and 36) measure a phase difference between the first and second output signals (V.sub.OUT1, and V.sub.OUT2) and a difference circuit (30) provides a difference value in accordance with the phase difference. The difference value cancels any phase shift due to time delays associated with the phase detectors (26 and 36). The difference value is fed back to a phase shift circuit (20) for adjusting the phase of the second output signal (V.sub.OUT2) and locking the first output signal (V.sub.OUT1) in-phase with the second output signal (V.sub.OUT2).

Phase detector circuit and method of phase detecting

A method is described for maintaining a constant Q in a voltage controlled oscillator (VCO) which is tuned over a broad frequency band. A tank circuit (111) sets a center frequency of an oscillator circuit (112). A variable reactance circuit (113) provides a variable effective reactance across the tank circuit (111) corresponding to an applied tuning voltage (117) for tuning the VCO. Resistive currents from the variable reactance circuit are rectified by a rectification circuit (120). A comparator produces a Q control voltage corresponding to the rectified resistive currents and a reference current Iref at a terminal (126) which is coupled to a variable resistance circuit (122) for supplying differential resistive currents to the tank circuit (111) which offset the resistive currents from the variable reactance circuit, thereby maintaining a constant Q in the VCO.

Constant high Q voltage controlled oscillator

A demodulation circuit (10) performs quadrature demodulation on an IF input signal. The IF input signal processes through a preamplifier (12) to one input of a mixer (14). The mixer output goes to first and second multipliers (20, 22). A VCO (24) generates an oscillator signal that processes through a first multiplier (26) and first and second dividers (28, 30) to generate in-phase and quadrature recovered carrier signals that are applied to second inputs of the first and second multipliers which in turn produce the in-phase and quadrature demodulated baseband signals. A switching arrangement (32, 38, 40) for the multiplier and dividers provides the proper frequency signal to a second input of the mixer to generate sum and difference frequencies. A filter and amplifier at the output of the mixer removes the summation frequency leaving the difference frequency to the first and second multipliers.

Quadrature demodulator operable over different IF frequencies

An active filter circuit (10) that has a cut off frequency being substantially independent of absolute and temperature variations due to on chip resistors (R.sub.1, R.sub.2 and R.sub.3) has been provided. The active filter includes a transconductance gain amplifier (16) having first and second currents (I.sub.B and I.sub.E) the ratio of which are controlled such that the absolute and temperature effects of any on chip resistors of the active filter circuit are removed. The ratio of the first and second currents of the transconductance gain amplifier are controlled by a circuit that generates third and fourth currents (I.sub.b and I.sub.e) which are a function of a bandgap voltage. The circuit then utilizes the third and fourth currents and provides, to the transconductance gain amplifier, a current that is substantially equal to the ratio of square of the third current to the fourth current, and a current substantially equal to the fourth current.

Stabilization circuit and method for second order tunable active filters

A quadrature detector FM demodulates an intercarrier signal operating at an unknown frequency. An LC tank circuit develops a 90.degree. phase shift across inputs of a multiplier. The output signal of the multiplier is amplified and fedback to control a reactance stage and adjust the reactive load at an input of the multiplier so as to maintain a predetermined phase relationship independent of the frequency of the intercarrier signal. A phase compensation stage removes any real component at the inputs of the multiplier also in response to the feedback signal.

FM demodulator with self-tuning quadrature detector

An AGC system for use in positive modulation schemes of video signals is provided. The AGC system utilizes an IF amplifier, a demodulator, a video amplifier, a gated amplifier and a peak detector. The gated amplifier has a first, relatively fast, time constant associated therewith. The gated amplifier, which is activated during the time interval that the black voltage appears on the video signal, is responsive to an intial reference voltage and to the video signal for providing an output signal to control the gain of the IF amplifier. The peak detector has a second, relatively slow, time constant associated therewith. The peak detector is used to detect the peak white voltage level of the video signal to adjust the initial reference voltage to account for fluctuations and errors in the peak white voltage level.

Automatic gain control system for use in positive modulation which

A phase detector is implemented with NPN transistors for providing a symmetrical push-pull output current operating in response to the phase difference between the falling edge of an oscillator signal and the mid-pulse of a sync signal. A current sinking circuit is responsive to the first and second input signals for providing a first current of predetermined magnitude and for sinking a second current of predetermined magnitude from the output of the phase detector. An NPN transistor current mirror circuit has an input responsive to the first current provided by the current sinking circuit and an output for sourcing a third current into the output of the phase detector, while a voltage equalizing circuit establishes substantially equal potentials at the input and output of the current mirror for maintaining proportional input and output current thereof.

Phase detector having all NPN transistors

A circuit for providing rapid charge and discharge of a capacitive load is utilized in conjunction with a phase detector error signal output generated in a television video demodulator system for controlling the operating frequency of the local oscillator. The circuit comprises a pair of comparators each biased to a respective threshold level whereby the first comparator provides an output signal when the error signal supplied thereto from the phase detector exceeds its threshold level and the second comparator provides an output signal when the error signal is less than its threshold level. An additional circuit is coupled to the outputs of the pair of comparators and is responsive to the first comparator for sourcing current to the capacitive load while being responsive to the second comparator for sinking current from the load. The capacitive load may be the AFC filter of an AFC loop of a television receiver wherein the local oscillator frequency is controlled by the voltage developed across the filter.

Slew enhancement circuit for an automatic frequency control system

A detection circuit for providing an error signal corresponding to the phase difference between applied input signals is described comprising a balanced multiplier input section for receiving the input signals and having a pair of outputs; a first switching circuit responsive to a switching signal for commutating the outputs of the multiplier section between first and second circuit nodes; a current turnaround circuit coupled between the first and second circuit nodes and third and fourth circuit nodes, a second switching circuit responsive to the switching signal for alternately coupling the third and fourth circuit nodes to a fifth circuit node and an output of the detection circuit; a current mirror circuit having first and second terminals and a third switching circuit responsive to the switching signal for alternately coupling the first and second terminals of the current mirror circuit to the fifth circuit node and the output of the detection circuit.

Phase detector

In a stereo television video demodulating system comprising an IF filter coupled via a limiter stage to a phase detector of a phase locked loop and further coupled to a video demodulator, a phase reduction circuit for reducing differential phase effects in the television which includes a capacitive circuit coupled between an output of the video demodulator and the multiplier section of the phase detector and a resistive circuit coupled between an output of the video demodulator and the multiplier section.

Differential phase reduction circuit for a video demodulating system and

An amplifier is provided for supplying a single output signal responsive to applied differential input signals applied to respective inputs thereof. The amplifier includes a differential input section having inputs coupled respectively to the inputs of the amplifier and a closed feedback loop including only NPN transistors which is coupled between the output of the differential input section and one of the inputs of the amplifier for providing a feedback signal to force the voltages at the inputs of the amplifier to be equal. In addition, the signal output signal is produced at an output of the closed feedback loop.

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Tempe, AZ, United States of America

Michael McGinn